The present invention relates to the field of communications, and, more particularly, to phased array antennas and related methods.
Antenna systems are widely used in both ground based applications (e.g., cellular antennas) and airborne applications (e.g., airplane or satellite antennas). For example, so-called xe2x80x9csmartxe2x80x9d antenna systems, such as adaptive or phased array antenna systems, combine the outputs of multiple antenna elements with signal processing capabilities to transmit and/or receive communications signals (e.g., microwave signals, RF signals, etc.). As a result, such antenna systems can vary the transmission or reception pattern (i.e., xe2x80x9cbeam shapingxe2x80x9d) or direction (i.e., xe2x80x9cbeam steeringxe2x80x9d) of the communications signals in response to the signal environment to improve performance characteristics.
As a result of technological advancements and the miniaturization element control circuitry, for example, the density of antenna elements in phased array antennas continues to increase. While significant advantages may be realized by having an increased amount of antenna elements within the same surface area, there are potential drawbacks to grouping a large number of antenna elements too close together.
In particular, when the main signal beam is steered at certain angles, signal side lobes may result with certain antennas. These side lobes may cause undesirable interference with the main signal beam. In certain circumstances, side lobes may even have an intensity or gain equal to that of the main signal beam, which are commonly referred to as xe2x80x9cgrating lobesxe2x80x9d, and are particularly problematic.
Attempts have been made in the prior art to reduce high gain side lobes and/or grating lobes in phased array antennas by varying the pattern of the antenna elements. One such approach is to use an aperiodic antenna element array. An example of a phased array antenna having an aperiodic array is disclosed in U.S. Pat. No. 6,147,657 to Hildebrand et al., which is assigned to the assignee of the present application. The antenna elements of the array have an unequally spaced circular distribution which decorrelates angular and linear separations among elements in the array. Without special correlation among the antenna elements of the array, side lobes are advantageously diminished.
While the phased array antenna structure described in the above patent provides a significant advancement in the art, one difficulty in working with aperiodic arrays, for example, is that the design necessarily changes as the number of antenna elements to be used changes. That is, when the number of antenna elements is changed from one design to the next, so too will the angles and relative spacing between the antenna elements change. Accordingly, aperiodic arrays are not easily scalable from one application to the next, and extensive ad hoc or re-design may therefore be required with each new application. Moreover, when using a relatively large number of antenna elements, calculation of the numerous angles and locations that may be required can be quite cumbersome.
Other attempts to reduce side/grating lobes have also been used in the prior art. For example, U.S. Pat. No. 5,838,284 to Dougherty discloses a phased array antenna including antenna elements arranged in the shape of a logarithmic (i.e., equiangular) spiral. While such a design may be less cumbersome to design than an aperiodic array, when such an antenna is used for beam steering it may still suffer from high gain side lobes or even grating lobes at wide scan angles.
Another related example may be found in U.S. Pat. No. 6,205,224 to Underbrink which discloses an array including antenna elements positioned on logarithmic spirals where the spirals intersect a plurality of concentric rings. Yet, while this approach may also help reduce side lobes, it may not be easily scalable from one design to a next where different numbers of antenna elements and varying amounts of surface area are available. Thus, significant design time may still be required with each new antenna array.
In view of the foregoing background, it is therefore an object of the present invention to provide a phased array antenna having an array which reduces occurrences of grating and/or high gain side lobes yet is relatively easily scalable for numerous applications.
This and other objects, features, and advantages in accordance with the present invention are provided by a phased array antenna which may include a substrate and a plurality of spaced apart phased array antenna elements carried by the substrate and arranged along an imaginary Archimedean spiral. More particularly, the imaginary Archimedean spiral may include a plurality of levels, and a spacing between adjacent pairs of phased array antenna elements along the imaginary Archimedean spiral may be substantially equal to a radial spacing between adjacent levels.
The imaginary Archimedean spiral may be defined by the polar coordinate equation r=axcex8N, where r is a radius, xcex8 is an angle, and a and N are real numbers, with N preferably being equal to 1. Additionally, the phased array antenna may have an operating wavelength xcex, and a spacing between adjacent pairs of phased array antenna elements may be less than about 10xcex. Further, the plurality of phased array antenna elements may have a substantially equal spacing along the imaginary Archimedean spiral, and the substantially equal spacing may also be less than about 10 xcex.
In particular, the plurality of phased array antenna elements may include greater than about 20 phased array antenna elements. Further, substantially all of the plurality of phased array antenna elements may be along the imaginary Archimedean spiral.
The phased array antenna may further include at least one controller for cooperating with the plurality of phased array antenna elements to provide beam steering. For example, the at least one controller may include a plurality of element controllers each connected to at least one of the phased array antenna elements, and a central controller connected to the plurality of element controllers.
A method aspect of the invention is for making the phased array antenna as briefly described above. The method may include providing a substrate and arranging a plurality of phased array antenna elements on the substrate along an imaginary Archimedean spiral. The Archimedean spiral may include a plurality of levels, and arranging may include setting a spacing between adjacent pairs of phased array antenna elements along the imaginary Archimedean spiral to be substantially equal to a radial spacing between adjacent levels.
More particularly, the imaginary Archimedean spiral may be defined by the polar coordinate equation r=axcex8N, where r is a radius, xcex8 is an angle, and a and N are real numbers, with N preferably being equal to 1, as noted above. Furthermore, arranging may include arranging the plurality of phased array antenna elements to have spacing between adjacent pairs thereof of less than about 10xcex, for example, where xcex is an operating wavelength of the phased array antenna. Moreover, arranging may include arranging the plurality of phased array antenna elements to have a substantially equal spacing along the imaginary Archimedean spiral, which may also be less than about 10xcex. A number of the phased array antenna elements may be in a range of about 20 to 200, for example. Also, arranging may include arranging substantially all of the plurality of phased array antenna elements along the imaginary Archimedean spiral.